Paperboard product and process for making same



June 17, 1952 w. F. GILLESPIE 2,601,114

PAPERBOARD PRODUCT AND PROCESS FOR MAKING SAME Filed Jan. 8, 1949INVENTOR: wfi

HIS ATTORNEYS.

Patented June 17, 1952 PAPERBOARD PRODUCT AND PROCESS FOR MAKING SAMEWilbur F. Gillespie, Bogalusa, La., assignor to Gaylord ContainerCorporation, St. Louis, Mo., a corporation of Maryland ApplicationJanuary 8, 1949, Serial No. 69,955

6 Claims. 1 This invention relates to a process of preparing newpaperboard products of high wet strength, abrasion and greaseresistance, especially designed for the fabrication of multiple tripcarriers including containers for bottled beverages prepared by aspecial process combining external and internal treatments. This processprovides, among other improvements, an outer board surface of highresistance to abrasion, frictional losses, moisture and greasepenetration under the most rigorous conditions of service.

An object of the invention is to provide a combined board having a wetMullen strength at least 50% of its 'dry strength, and an outer surfacehighly resistant to abrasion or scufllng under both wet and dryconditions and possessing excellent printing properties.

Another object is to provide a linerboard having its outer or exposedsurface resistant to soiling by grease, dirt, and other extraneoussubstances so that the attractive appearance of shipping containersmanufactured therefrom will be preserved during their normal life.

Another object of the invention is to provide a solid fibre laminatedboard suitable for fabricating multiple trip beverage carriers having aminimum dry Mullen test of 550 pounds per square inch, and a Wet Mullentest of not less than 300 pounds per square inch after immersion inWater at 75 F., for twenty-four hours according to the JAN- 108specifications of the Army and Navy and an outer or exposed surface ofvery high resistance to abrasion or scuffing under both wet and dryconditions, combined with excellent p-rintability and soilingresistance.

Further objects of the invention will appear from the description andexample of the process and the appended claims.

The use of fibre containers suitable for transporting bottled beveragessuch as beer, soft drinks, and the like, from the manufacturers orbottling plants to the dispensers and consumers of such products, andwhich may be returned to the beverage supplier for ten to fifteen ormore refillings and return trips, is extensive and rapidly increasing.Such containers are known in the trade as multiple trip carriers. Fibreboxes for this purpose have important advantages over metal strappedcarriers made of wood. For example, the standard twenty-four 12-oz.fibre boxes are from four to eight pounds lighter in weight than woodenboxes of similar carrying capacity, with resulting savings intransportation expense. They have the additional advantages ofeliminating re-cocpering costs and the personal injury hazard involvedin the use of metal strapped wood cases.

Present multiple trip fibre carriers are ordinarily constructed of 3 to5-ply laminated solid fibre blanks, comprising inner filler sheets andtwo liners. The natural lively color of kraft board imparts anattractive pleasing appearance to the package. The walls of the caseprovide an excellent means for printing the manufacturers advertisingmatter.

The outer liner of the solid fibre sheet on present multiple tripcarriers is usually coated with paraffin or similar oil or wax basematerial to provide partial resistance to moisture penetration underhigh relative humidity and the usually weathering conditions to whichsuch carriers are necessarily subjected. Such coatings, however, havevery slight resistance to abrasion so that in the course of the severewear and tear to which multiple trip carriers are subjected, theprotective coating usually cracks and becomes partially scuffed from thecorners and especially the bottom of the box, thus destroying anymoisture resistance of the container, which is then subject to rapiddeterioration under conditions of high relative humidity or partialexposure to Water.

Parafiin or similar oil or wax base coatings detract from the brilliancyof both printing and the attractive natural color of the board, thusadversely aifecting the advertising value and. appearance of the case.Such coatings are greasy to the touch and have a pronounced tendency topick up foreign material, dirt, and the like, so that the case,including the printing, soon becomes unsightly and unfit for furtheruse. Another objection to paraflin and similar coatings is theirtendency to rub off and soi1 any material with which they come incontact, including clothing and other fabrics.

when loaded with beverage products to withstand crushing or collapsewhen stacked ten or twelve high in trucks or railroad cars. In addition,sufficient structural rigidity of the case should be maintained underextreme weather conditions during transportation and other con-' ditionsincident to normal use to prevent failure or collapse. Ordinarilycarriers of the usual construction, when exposed to high relativehumidity or to water for any appreciable length of time, will undergoply separation of the laminated solid fibre board. This in turn promotesabsorption of water by capillary attraction throughout the fiberstructure with consequent loss of rigidity and permanent damage to thecontainer.

Thus a solid fibre laminated board, suitable for fabrication intoserviceable multiple trip carriers, must meet several exacting physicalrequirements to insure satisfactory functioning of the boxes fabricatedtherefrom throughout their normal life in multiple trip service.

This invention teaches a process of preparing a new paper board productcomprising a series of balanced specific treatments applied to selectedcellulosic fibres during the process of sheet formation, calenderfinishing, and lamination into multi-ply board, whereby specificphysical properties are imparted to the combined sheet. Each of thetreatments is essential and the combination of the coordinated seriespractically overcomes all of the foregoing objections and deficienciesfound in present multiple trip carriers constructed of the bestcommercially available solid fibre board.

The linerboard of this invention may be formed of chemical pulp derivedfrom long, strong fibered wood, carefully digested and refined forproducing maximum strength properties. It may be of any desired weightand caliper, depending upon the purpose and use of the containersmanufactured therefrom. For example, the liner for combined fibre-boardsuitable for multiple trip bottle carriers may be an 80 pound, .022caliper sheet containing substantially 100 percent of said high strengthchemical pulp. During the manufacturing process a rosin size is appliedto the liner in sufiicient quantity to insure an average absorptionnumber not exceeding 350 according to the standard method hereinafterdescribed.

The next step in the process is to concentrate an abrasion resistant andwet strength imparting resin composition in one or more of the outerplies of the linerboard. A suitable resinous composition for thispurpose is a melamine formaldehyde condensation product, such as thatknown in the trade as Parez #607. Other resinous compositions, wellknown to those skilled in the art, such as, urea formaldehyde, will alsogive satisfactory results. These other compositions may be used inappropriately varying proportions, by weight, to obtain results similarto those with the use of the melamine formaldehyde condensation product.

I have discovered that by concentrating a sufficient amount of theresinous composition in one or more of the outer plies of thelinerboard, a wet Mullen test of the laminated board at least percent ofthe dry Mullen strength will be assured. The introduction of thisresinous composition as described, substantially supplements the naturalbonding of the outer fibrous layers of the sheet, thereby greatlyincreasing the strength, toughness or scuff and abrasion resistance ofthe board in the outer surfaces, that is, in the region which issubjected to the most severe frictional wear when the laminated sheet isfabricated into a container.

I am aware that the addition of melamine and other wet strength abrasionresistant type resins to the furnish in paper-making have beenadvocated, but the method of applying such resins has been to uniformlydisperse them throughout the sheet, whereas in my invention, the resinsare concentrated in or near the surface of the sheet to attain suitablehigh wet Mullen strength and abrasion resistance in only those areaswhere these properties are essential for the objectives of my invention.The concentration of resin in the outer plies of the liner acts as apartial barrier to lateral water penetration into the remaining plies ofthe liner. This step of the process in combination with a specialcalender treatment and a water insoluble bonding of the liners andfillers into the combined board, to be hereinafter described, in turnreduces the water penetration into the inner filler sheets substantiallyso that a high wet strength of the laminated board is obtained with theuse of a relative very small amount of resin.

This novel means of obtaining the high wet strength objective withoutincurring the prohibitive cost of distributing a sufficient quantity ofthe resin throughout the liner to obtain equivalent results, is one ofthe important features of my invention. It furthermore fulfills anotherimportant objective of concentrating the abrasion resistant resin injust that part of the liner which is subject to severe frictionaldamage, namely, the outer surface.

A further treatment is given to the linerboard at the calender stacks toimprove the water and grease resistance and still further improve theresistance to abrasion or scuiiing. A unique combination of chemicalsfor this purpose, constituting an important feature of the invention,consists of a thin boiling starch, dimethylol urea and polyvinyl alcoholin an aqueous solution. Without being able to precisely define thechemistry involved in this combination which imparts unexpected,valuable and essential properties to the outer surface of the liner, itis believed that the thin boiling starch re-acts with the dimethylolurea to form a compound highly resistant to abrasion and moistureresistance, in these respects supplementing the properties imparted tothe board by the previously described resin treatment, and the polyvinylalcohol component increases the resistance to grease penetration andsoiling, thus preserving the original attractive appearance of thelinerboard.

In addition, the calender treatment with the described combination ofchemicals imparts a smooth finish of excellent printability to thesurface of theliner. The board retains its characteristic bright colorin contrast to the inferior printing surface and unattractive color ofthe board which characterizes the paraffin coating usually applied toboard for containers of the class described.

The next step in the process of preparing fibreboard suitable formulti-trip carriers is to prepare a filler sheet which may be, forexample, a pound, .025 caliper board, with a furnish controlled to meetthe required test specifications, A rosin or wax size or a combinationof sizes is applied to the filler sheet in sufficient quantities toinsure an absorption number of not more than an average of 350.

Filler sheets and an inside and outside liner, prepared as described,are combined into a multiply solid fibre board with an adhesivecomposition capable of formingan irreversible pletely' water insolublegel.

After submergingin water for a minimum of twenty-four hours, accordingto the JAN-P-108 specifications of the Army and Navy, this laminatedsheet will have a Mullen test at least of the value before submergenceand will show no separation of the component plies. It has an abrasionresistance even when wet several times that of ordinary solid fibreboard so that shipping containers fabricated therefrom will withstandfar more wear and tear over Wet concrete floors, for example, and othersevere conditions of use, than boxes made from the usual quality ofsolid fibre board.

The combined sheet has a dry G. puncture test of at least 550 inchounces and a test after submergence in water of not less than 450 inchounces, or 80% of the dry. It has a coefficient of friction within therange found to be satisfactory for commercial purposes, namely, .275 to.350 determined by the method hereinafter described.

Multi-trip carriers made from the combined board described have a usefullife'at least 50% greater than boxes made from the best commercial solidfibre grades now available. This feature insures important economies tothe users of such containers.

and com- Furthermore the special finish to the exposed surface of theboard preserves the original natural color so that the attractiveappearance of the carrier is maintained to a high degree even afterre-use twenty or more times.

The liner produced by the process of this'invention may be bonded tocorrugating medium to form corrugated board having similar enhancedproperties. It may also be used in the manufacture of other laminatedproducts with correspondingimproved resistance to frictional losses, andincreased useful life under extreme conditions of relative humidity.

Having thus set forth the general aspects of my invention, I willdescribe one form by an example for producing a solid fibreboardsuitable'for fabricating multi-trip bottle carriers of greatlyimproved quality. It must be understood that this example isillustrative of one form of my process and that my invention is notlimited thereto but may be varied therefrom by the use of resinousmaterials other than melamine formaldehyde condensation products, andmaterials giving equivalent results in the calender treatment of thelinerboard, and laminating adhesive compositions other than soyaprotein, in quantities, concentrations, etc., falling within the purviewof the appended claims, may be employed if desired.

In the accompanying drawings which form a part of this specification,

Fig. 1 represents a simplified diagrammatic side elevational view,partly in section, of a cylinder machine illustrating my process for mypaperboard product. i

Fig. 2 represents a simplified diagrammatic side elevational view partlyin section of a Fourdrinier machine illustrating my process for mypaperboard product.

The cylinder machine includes whipper I, cylinders 2 for liner stack,cylinders 3 for filler stack, couch roll 4, press sections 5, dryersections 6, first calender stack 1, calender dryers 8, and secondcalender stack 9.

The Fourdrinier machine includes headbox l0, breast roll H, table rollsl2, dandy 'roll l3,

suction boxes [4, return wire roll l5, wire [6, suction couch roll ll,lump breaker roll l8, dryer sections l9, first calender stack 20,calender dryers 2|, and second calender stack 22. The machineshereinbefore described are of a well known type and it is consideredunnecessary to illustrate them in detail.

Following is an example ofthe preferred practice in carrying out myinvention:

Step 1.An pound,-.022 caliper linerboard sheet. testing 150 pounds persquare inch, is prepared on a cylinder machine from high strengthsulphate pulp derived from strong, long fibered wood, sized in the usualmanner with '75 gallons of a 5% solids rosin size solution per ton ofboard.

The amount of size specified will insure an average absorption number ofthe board of not more than 350.

The pH of the'stock is adjusted to between 4.0'and 6.0.

Step 2.--The linerboard consists of five. (5) plies. The two outer pliesare treated with from 1% to 5%, by weight, of a melamine formaldehyderesin, such as that known by the trade name of Parez #607. The resinsolution enters with the stock at A in Fig. 1. I have found that 3.5% ofthe resin gives very satisfactory results. When the board is prepared ona Fourdrinier machine, the required amount of resin enters with thestock at the secondary headbox B in Fig. 2.

The resin is prepared for use by mixing in a hydrochloric acid-watersolution so that a final composition contains about 12% of the resin, byweight, and has a molar ratio of hydrochloric acid to the melamine ofapproximately 0.8. After thorough mixing, the solution is allowed to agefor approximately twelve hours at its mixed concentration. It is thenmetered to the stock slurry at its mixed concentration or furtherdiluted with water if desired. In the case of the cylinder machine, thepoint of addition to the stock should be as near to the cylinder headboxas possible. In Fourdrinier machine application, the addition is made tothe stock going to the secondary headbox, or in the secondary headbox.At the customary temperature to which the board is raised as it passesthrough the driers, the resin is polymerized or cured, therebyincreasing the natural bond of the fibers in the two outer plies of theboard. This increased bonding of the outer fibers results in an overallincreased tensile strength of the board, greatly increased resistance toabrasion or scuffing and at least a increase in the wet Mullen strengthof the treated board as compared to the wet Mullen strength of theuntreated board.

Step 3.As an additional protection to the surface of the liner, and toimpart improved moisture and grease resistance, a novel chemicalcomposition is applied to the board on the calender stacks at C in Fig.2, and at a corresponding point D in Fig. 1 in the case of a cylindermachine. The unique treatment comprises the reaction product of acombination of a thin boiling starch, which is a product well known tothose skilled in the art, dimethylol urea and polyvinyl alcohol.

The composition is prepared as follows:

Water gals 75 Thin boiling starch, an example of which is Starch' Rsupplied by Penick and Ford lbs 100 Dimethylol urea lbs 25 Polyvinylalcohol lbs 25 aooi ns hes ngred en s e he to 1 and the pI-I adjusted toabout 4.0 with paper maker s alum. The mixture is agitated about thirtymin: utes and then diluted with water to a volume of p roximate 100 ga os n the p a ain e J'llsted to 5.5-6.0 by the addition of an alkali. Thismixture is applied at the calender stacks at a rate that will consumeapproximately 3.0 pounds of solids of the starch resin composition nd1.6. ounds o o v nyl. oh l e on of treated stock. This treatment impartsgreatly increased resistance to abrasion under both wet and d e nd t e eand en m o m n n 015- ture resistance to the treated layers of theboard, whil the pr ncip un t on. o he l v n e cohol is to improve theprintability of the outer surface and increase its grease and soilingresistance. The quantity of solution per ton of board treated may bevaried within reasonable limits; I have found that the amount specifiedabove gives satisfactory results; and any substantial reduction in thequantities reduces the eifectiveness of the treatment, while increasedquantities are unnecessary for the proper functioning of the board forthe purposes intended.

Step 4..+The filler sheets are prepared on the cylinder machine in theconventional manner with kraft pulp derived from long, stron fiberedwood, carefully digested and refined for obtaining maximum strengthproperties, with a furnish controlled to meet the required testspecifications. The filler is a 90 pound sheet, caliper .025, testing110 pounds per square inch. It is sized with not less than 75 gallons ofa rosin or wax size or a combination of sizes to insure an averageabsorption number of the sheet of not more than 350.

Step 5.-A 4-ply solid fibre board is made on the conventional laminatingmachine or paster by gluing two filler sheets with a front and backliner with a liquid adhesive composition which forms a water insolubleirreversible gel upon setting. An adhesive composition entirelysatisfactory for this purpose is described in pending application forLetters Patent, Serial #44,164, filed August '13, 1948, by J. J. Koeniget al., now Patent No. 2,597,006. This adhesive composition isessentially a soya protein base glue dispersed in an aqueous medium withpotassium hydroxide or other dispersing agents.

Other water insoluble adhesives may be used in forming the combinedboard, such as poly.- vinyl alcohol compositions and the well knownstarch urea glues, but I have found that the protein base adhesive ismore satisfactory, both from cost and operating standpoints. Accordinglymy preferred practice is to prepare the adhesive for use on thelaminating machine in the l w n manner Sftep 1.--Six hundred andsixty-five (665) galions of water are run into amixing tank equippedwith efficient agitation and means for tempera: ture control. The wateris brought to a temperature preferably of about 80 F. While thetemperature of the, water may be varied within reasonable limits, forexample, between 70 F. and not exceeding 100 F., cooler water tends todelay the dispersion of the proteins, and-water of higher temperaturesaccelerates hydrolysis oi the protei c n and shou be a o Step2.--Agitation is maintained throughout the p ep n o he adhe v o o isince, as ingredients are added, a thixotropic suspension is formed,whichrequires continued agitation to maintain uniform consistency.

-Qn a on. of s am d st ed n .1 is added, which acts as wetting agent forthe dry ingredients subsequently added and reduces the viscosity of thefinished adhesive, thereby enhancing its spreading and flowingcharacteristics.

Step 4.--.-Eighteen hundred pounds (1800 lbs.) of Klondyke DRG clay areadded.

Step 5.-Afte r the clay has been thoroughly mixed with the water, "42pounds of sodium pentachlorophenate dissolved in 15 gallons 'of waterare added. This material is a fungicide and preservative for protein andcarbohydrates and is added at this stage because, being stronglyalkaline, it aids in the dispersion of the clay par ticles and thickensthe dispersion slightly. It is also an aid, due to its alkalinity, inpeptiz'ing the ubsequen l added P o e n Step 6.?Add 1600 pounds of soyaalpha proein, ef rabl o a i c i of 350 t .500 mm;- noises;-

ten t h addit n of the e nh P tein, agitation should be maintained forminutes to insure thorough wetting and dispersion of th nr tem ar i es.-

Step 8.-.-One hundred and twenty-eight pounds .2. l s of p tass um. hdrox d s ed in. 59 a n f wa r. re adde s a y s ss le upon the completionof the mixing of the protein and clay. The mixture will be observed tothicken immediately after the addition of the t si m h ro de. ndcontinues t thie en until peptization is complete. During this step inthe process, the protein particles swell into translucent globules andfinally rupture. The clay particles likewise apparently break down andform colloidal combinations with the protein and potassium hydroxide,since no clay particles can be discovered when a thin film of thefinished composition is examined under a microscope at 100 diametersmagnification. Distinct advan: tages result from the addition of theclay in advance of the proteins. This practice insures a maximumdispersion of the clay and avoids any tendency to form lumps, such asoccur when the clay is added simultaneously with the protein orsubsequent to the protein. In addition, it is believed that the clayparticles act as an aid to the complete dispersion of the protein by agrinding action on the. surface of the protein particles, thus exposingmore and more protein surface to the action ofthe subsequently addedalkali solution.

Step 9.Peptization of the protein is completed inthirty minutes afterthe addition of the alkali solution. A suflicient amount of water isthen added tobring the. volume to exactly 1056 gallons durin continuousagitation. The temperature throughout the preparation of the mixture iscontrolled to between 70 and 100 F. Upon completion of the batch, thetemperature is adjusted to between and F., and is then ready for use.Because of the thixotropic nature of the adhesive, it should bemaintained in motion at all times, including storage, by mild agitation.

This adhesive Solution is applied on the laminating-qmachine to thecomponent liner and filler sheets at the rate of approximately onegallon or less per M square feet of glue line, or three allons per Msquare feet of the consolidated 4- pl b ers e ombine boa hu P e aredwill showno ply separation whatsoever after being subjected to theArmyand Navy JAN.P-.-.'108 test. which provides for immersion in waterat 75 for t nt fonr h r The board has a minimum Mullen test of 550pounds per square inch, and not less than 300 pounds per square inchafter twenty-four hours immersion in water according to the JAN-P408specifications. It has a puncture test in its dry state, measuredaccording to the G. E. standard method, of at least 550 ounces per inchof tear, and after immersion in water of 450 ounces per inch of tear.

The greatly increased resistance to abrasion and soiling is illustratedby the test of the typical commercially available multiple trip bottlecarrier fabricated of solid fibreboard coated with paraffin. The testwas made by placing three of the typical paraffin coated containers andthree containers of the same dimensions made of fibreboard producedaccording to the process of my invention in the standard revolvingdrums, described in TAPPI standard T 800 sml l.

The lids on both types of containers were closed and sealed. A greasy,sweeping compound, together with floor sweepings were introduced intothe drum, thus both types of boxes were exposed to the same wear andsoiling conditions. The drum was revolved 12,870 times at the rate of 3or 4 R. P. M.

At the conclusion of the test two of the standard paraflin coated boxesfell completely fiat, the vertical corners having worn throughcompletely. The third paraflin box was in almost as dilapidated acondition, the sides barely hanging on. All three of the old style boxeswere unfiit for any further use.

The boxes fabricated from'the fibreboard of my invention, after the12,870 revolutions of the drum were still within about 80% of theiroriginal condition. They had sustained scuffed edges and. slightlyrounded corners, but all were still in good serviceablecondition.

The standard paraffin boxes were badly soiled with dirt and filthadhering to the surfaces, even though practically all of the paraffinwax had penetrated into the board. All corners and edges were badlyscuffed and dirt had been picked up by the loose fibers. All three ofthe boxes were soiled and scuffed beyond any further use.

The boxes fabricated from the fibreboard of my invention showed someslight soiling at the corners and edges where the fibers had been ruffedup. able condition and of far better appearance than the standardparaffin coated containers.

Another physical factor which is important in solid fibreboard for thepurposes described is the sliding resistance. This condition of thesurface of a combined board is usually expressed as a coeflicient offriction determined by the method hereinafter described. A lowcoefficient of friction results in cases due to slippage of stackedsheets and the containers fabricated therefrom, L

while a high coefficient of friction increases the labor of handlingboth the sheets and the containers made therefrom. The combined board ofmy invention has a coefficient of friction which has been found quitesatisfactory in practice, between 250-350.

The board is eminently satisfactory for fabricating multiple tripcarriers capable of twentyfive or more loaded trips under the mostsevere transportation and weathering conditions.

The linerboard prepared by the process of my invention at the end ofStep 4 of the foregoing example of my process, is suitable and may beused to advantage for purposes other than forming the laminated boarddescribed in the All three boxes were still in a highly use- Mullen orbursting strength TAPPI official standard test T-403 m-45.

Puncture test TAPPI tentative T-803 m-44.

Water immersion test The joint Army and Navy specification JAN-P- 108,entitled Packaging and Packing for Overseas Shipment by Boxes,Fibreboard (V-board W -board) Exterior and Interior.

The conditions of immersion are described on pages 6 and 7 of thespecification under paragraph headings:

Sliding test, expressed as coeflicient of friction This test is madeaccording to the following procedure:

Obiect.The object of this testis to measure the resistance of a coatedsurface to slipping or sliding.

Apparatus-A variable inclined plane.-This consists of a 13" x 13" boardpivoted at one'end to a base. The loose end of the board is providedwith means for raising it at a constant speed of 8" per minute. Avertical scale (inches by sixteenths) is attached to the base 5 from thepivot point.

Procedure.-The variable inclined plane is placed on its lowest position.A 12" x 12" sample of the coated material is attached (coated side up)to the-movable plane so that the direction of slide when the angle ofthe plans is increased will be along the machine or fibre direction ofthe material. Another 12" x 6" sample is folded around a 12# iron weightin such a way that a 6" x 6" coated area is fiat under the weight. Thisweighted sample is then placed on the sample attached to the movableplane so that the fibre directions are parallel and the coated faces aretogether. The mechanism for increasing the angle ofinclination isstarted. As the inclination increases the scale reading at the level ofthe moving board is watched, and at the instand the Weighted samplebegins to slide over the stationary sample, the scale is read to thenearest sixteenth of an inch.

Good averages may be obtained by testing three sets of samples of thesame materials five times per set and taking a grand average.-

The average reading thus obtained is an index of how the materialresists sliding, which is an important factor in the trucking andstacking operations.

It is only necessary to measure the vertical a 1-1 risebecause it isdirectly proportional to the 'co= eincient of friction. I From thedataderived bythe procedura the coe'flieien't of friction is calculated bythe well known methods.

Absorption number This test is made by the following method, which iswell known and generally recognized in the paperboard industry.

6" x 6" samples of the components to be .tested are immersed verticallyin water at 75 F., for ten minutes, after which the samples are removedfrom the water, the excess surface water is removed by blotting, and theweight gained during the immersion is calculated. This Weight gainexpressed in centigrams is known as the absorption number.

WhatI claim is: i v, h u

, A composite u antie us a a r d .L i wet strength solid fiberboardconsisting of permanently adhered to ether opposed outer liner sheetswith a substantially co-extensive filler sheet therebetween, a waterresisting jrosins'ize substantially uniformly distributed throughout allof said sheets, and, in part, serving to retard water penetrating theedges of the solid fiberboard by capillary attraction, the liner sheetsbeing composed of at least 'three plies, a water insoluble adhesivepermanently securing the inner-most ply of each liner sheet throughouttheir entire area to the adjacent side face of the filler sheet, and awater and abrasion resisting resin substantially uniformly distributed,along with the rosin, only throughout each of the outermost plies of theliners, thus supplementing the bonding of said pliesandserving toLdoubly retard iwater penetrating the exposed surfaces of the liners.

2. ,5 composite substantially stable, rigid, high wet strength solidfiberboard consisting 'of per- 1in enny adhered together opposed outerliner s with a substantially co-exte nsive filler :she'et therebetween,a water resisting rosin size inan amount tolinsure, an averageabsorption number of about 350 substantially uniformly distributedthroughout all of saidsheets, and, in part, serving to retard Waterpenetrating the :edges of the solid fiberboardbycapillary attraction,theliner sheets being composed of at least three plies, a waterinsoluble adhesive perma- In ntlysecuring the inner-most'ply of'eachliner sheet throughout their entire area to the adjacent side face ofthe filler sheet, and a water and abrasion resisting resin;substantially unif rml i r but al ih nrgs nijon y th ou h u h o ot r e-P ie 9 th iin'els, and 'intheratio of 1% to by weight with respect tothe treated liner plies, thus supplementing the bonding of saidplies andserving to doubly retard water penetrating 'the ex- "posed surfaces ofthe liners.

an composite substantially stable, rigid, high 'wet' strength solidfiberboard 6f not less thanfsoet 'oiits 'dry bursting strength csnsisun'ofpema- 'nently adhered together opposed outer liner sheets with twosubstantially co-extensive filler sheets therebetween, a water resistingrosinsize in an amountt'o insure an averagefabsorption number of about350 substantially uniformly distributed throughout an or said sheets,and, in part, serving to retard water penetrating the-edges of the solidfiberboard by capillary attraction,

the in r. sh ts b n p s at a le 'tf 'h plies, a water insoluble adhesiveperman'entlyse- 12 in eia ia a e th fi l fr sl etsjend theinner-in'ost'ply of each li ner sheet throughout their entire area totheadjacent side face 'ot the filler sheet and a water and abrasionresistin resin substantially uniformly distributed, along with therosin, only throughout ea'ch oithe outermost plies of the liners, and inthe ratio of l 7 to 5% by weight with respect to the treated liner P iet su plem n i afim .tb 'ii'iis s pl e a d ervin ..id.b b r t r Wa r ene.e. xro seriee s wel ee i t.

I 4'. The process of makinga composite substant a' lr b e rigid, i We?Str n th. s be bo d cd 'ris nsmi i 's ei rl n x s p n te t r e rm nedamb s bi. ll ilej i fibrous "material and rosinsize to form a slurry,with the rosin si'ze 'unifo rmly distributed therein, providing separatesources of the slurry, introducing a water and abrasion resisting resininto one source of the slurry, simultaneously forming and unitingindividual outer plies 'o'f fibrous material from said'one'souroe, andforming and unitingan inner ply from another source containing only thefibrou material and rosin, uniting all of the said plies to form linersheets, forming a filler sheet from the slurry containing only thefibrous'lnaterial androsin, disposing the filler sheet between opposinginner plies of two liner sheets, and permanently joiningthe said sheetstogether with a water insolubleadhesi ve. v '5. The process of making acomposite substantially stable, 1'igid,'high Wet strength, solidfiberboard comprising mixing a preponderance of 'wa te withpredetermined amounts of cellulosic fibrous materiarandro'sin size toform a slurry, with the rosin size in an amount to insure an averageabsorption number of aboutEbOuniformly distributed therein, providingseparate souro'es of the slurry, introducing a water and abrasionresisting resin in the ratio of 1% to 5% by weight with respect to thetreated liner plies into one source oi theslurry, simultaneously formingand uniting individual outer plie fibrous'inaterial from said onesource, and forming and uniting an inner'ply from another sourcecontaining only the fibrous materialand rosin, uniting all of th'e saidplies to formliner sheets, forming a filler sheet from the slurrycontaining only the fibrous material and rosin, disposing the fillersheet betweenopposing inner plies of two liner sheets, and permanentlyjoining the said sheets together with a water insoluble adhesive, r

6. The process of making a 'composite substantially stable, rigid, highWet strength, 'soiid fiberboard of notless thanbi ib of its dry burstingstrength comprising mixing a preponderance of water, with predeterminedamounts of cellulo si c fibrous material and rosin size to form aslurry, withthe rosin size in an amount to insure an average absorptionnumber of about 350 uniformly distributed therein, providing separatesources of the slurry, introducing a water and abrasion resisting resinin the ratio of 1% to'5% by weight with resp'ect to thetreatedlinerplies into one source of the slurry, simultaneously 13 Imost ply of each of the said liner sheets together with a waterinsoluble adhesive.

WILBUR F. GILLESPIE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Name Number Date 10 1,438,966 Perry Dec. 19, 19222,050,382 Rowbotham et a1. Aug. 11, 1936 2,271,620 Brier Feb. 3, 19422,322,887 Schwartz June 29, 1943 Number Name Date 2,352,293 Sherman June27, 1944 2,385,714 La Piana Sept. 25, 1945 2,399,489 Landes Apr. 30,1946 FOREIGN PATENTS Number Country Date 119,092 Australia Oct. 16, 1944OTHER REFERENCES Industrial 81 Engineering Chemistry, July 1942, pages817-820, Soybean Protein Adhesive Strength and Color, by A. K. Smith andHerbert J. Max.

4. THE PROCESS OF MAKING A COMPOSITE SUBSTANTIALLY STABLE, RIGID, HIGHWET STRENGTH, SOLID FIBERBOARD COMPRISING MIXING A PREPONDERANCE OFWATER, WITH PREDETERMINED AMOUNTS OF CELLULOSIC FIBROUS MATERIAL ANDROSIN SIZE TO FORM A SLURRY, WITH THE ROSIN SIZE UNIFORMLY DISTRIBUTEDTHEREIN, PROVIDING SEPARATE SOURCES OF THE SLURRY, INTRODUCING A WATERAND ABRASION RESISTING RESIN INTO ONE SOURCE OF THE SLURRY,SIMULTANEOUSLY FORMING AND UNITING INDIVIDUAL OUTER PLIES OF FIBROUSMATERIAL FROM SAID ONE SOURCE, AND FORMING AND UNITING AN INNER PLY FROMANOTHER SOURCE CONTAINING ONLY THE FIBROUS MATERIAL AND ROSIN, UNITINGALL OF THE SAID PLIES TO FORM LINER SHEETS, FORMING A FILLER SHEET FROMTHE SLURRY CONTAINING ONLY THE FIBROUS MATERIAL AND ROSIN, DISPOSING THEFILLER SHEET BETWEEN OPPOSING INNER PLIES OF TWO LINER SHEETS, ANDPERMANENTLY JOINING THE SAID SHEETS TOGETHER WITH A WATER INSOLUBLEADHESIVE.